1. Field of the Invention
The present invention relates to an air conditioner, and more particularly, to a multi-unit air conditioner and a method for controlling the same which are capable of preventing continuous introduction of a refrigerant into an indoor unit or indoor units in an OFF state, thereby preventing a degradation in the cooling and heating efficiencies of the air conditioner.
2. Discussion of the Related Art
Generally, air conditioners perform procedures of compressing, condensing, expanding and evaporating a refrigerant to cool and/or heat a confined space. Such air conditioners are classified into a cooling type wherein a refrigerant flows only in one direction through a refrigerant cycle, to supply cold air to a confined space, and a cooling and heating type wherein a refrigerant flows bi-directionally in a selective manner through a refrigerant cycle, to selectively supply cold air or hot air to a confined space.
Also, such air conditioners are classified into a general type wherein one indoor unit is connected to one outdoor unit, and a multi-unit type wherein a plurality of indoor units are connected to one outdoor unit. For the multi-unit type, an air conditioner may be implemented which includes at least one outdoor unit.
Multi-unit air conditioners are classified into a switching type wherein all indoor units operate in the same operating mode, that is, in cooling mode or heating mode alone, and a simultaneous type wherein a part of the indoor units operate in cooling mode, and the remaining indoor unit or indoor units operate in heating mode.
In such a multi-unit air conditioner, a controller is provided at each of the indoor units and outdoor unit. Through communications between a microcomputer included in the controller of the outdoor unit and a microcomputer included in the controller of each indoor unit, the outdoor unit controls the indoor unit. Also, each indoor unit is electrically connected in parallel with the outdoor unit such that the outdoor unit and indoor units are simultaneously powered on or off. The outdoor unit also controls the power ON/OFF of each indoor unit.
An electronic expansion valve is arranged in a refrigerant line extending to each indoor unit, in order to prevent the refrigerant from entering the indoor unit when the indoor unit does not operate. When the indoor unit operates, the electronic expansion valve allows introduction of the refrigerant into the indoor unit, and reduces the pressure of the refrigerant to expand the refrigerant to a low-temperature and low-pressure mist state.
Meanwhile, if necessary, power controllers may be installed in the indoor units, respectively, in order to individually control the power ON/OFF of the indoor units. In this case, however, there may be a problem in that, when a fraction of the indoor units are powered off during operation of the air conditioner, the electronic expansion valves connected to the powered-off indoor units can be no longer controlled from an open state thereof.
That is, when one indoor unit is powered off during operation of the air conditioner, the electronic expansion valve connected to the indoor unit can be no longer controlled from an open state thereof, so that the refrigerant is continuously introduced into the powered-off indoor unit. In this case, the performance of the other indoor units, which operate normally, is degraded, thereby causing a degradation in cooling and heating efficiencies. Furthermore, since no heat exchange is carried out in the powered-off indoor unit, the refrigerant, which does not perform heat exchange in the powered-off indoor unit, is introduced into a compressor. As a result, a degradation in the performance of the air conditioner occurs.